Two-photon polymerisation (2PP) is a relatively new additive manufacturing technique (AMT) that is able to fabricate structures with resolutions down to 100nm.
‘As this technique is the first true 3D lithography, it is not necessarily limited to a layer-by-layer fabrication process and it is thus capable of embedding and connecting objects in 3D,’ Jan Torgersen of Vienna University of Technology told The Engineer.
The team starts with liquid resin, which is polymerised at precise points by an fs-pulsed laser (usually emitting at 800nm) leaving behind a line of solid polymer.
In contrast to other AMTs, it is not necessary to prepare the working surface and overhangs can be produced without the need for supporting material.
Previously, the bottleneck of 2PP was the long processing time. To fabricate parts visible without a microscope, several days of structuring was necessary, with typical process speeds of around 100µm/sec.
Using novel photopolymerisable systems and a new mechanical setup, the Vienna team was able to increase this to 5m/sec.
Specifically, it uses continuously moving mirrors whose acceleration and deceleration periods have to be tuned very precisely to achieve high resolution at speed.
‘The specimen is quite a distance away from the mirrors. If the mirror just moves a little angle, quite a large movement is done on the specimen. This is how it gets so fast,’ Torgersen said.
Such speed could allow the routine manufacture of waveguides for optoelectronic applications and biomedical surfaces.
‘The technique is precise enough to make parts resembling the 3D biological environment; depending on the geometry of the scaffold and the type of cell, custom-made biological tissue can be made,’ Torgersen said.
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